1. Field of the Invention
The present invention relates generally to a vehicle which is powered by the power from a driving source. More particularly, this invention relates to a driving power control apparatus for a vehicle, which controls driving power according to the acceleration of that vehicle requested by the driver.
2. Description of the Related Art
In general, vehicles are demanded to run under various environmental conditions and are each manipulated in different ways by different drivers. And, with respect to the behavior of the vehicles, there are demanded responding properties and smooth actions intended by the individual drivers. With regard to the behavior of the driving power in each vehicle, it is known that the action of an engine-mounted vehicle, for example, is controlled in accordance with the amount of the accelerator pedal thrust by the driver.
For instance, in the conventional control apparatus disclosed in Japanese Unexamined Patent Publication No. Hei 1-294925, the following control technique is employed. To describe in detail, in this control apparatus the throttle valve disposed in the intake passage of an engine is opened or closed by the actuator. The value of the target acceleration intended by the driver is predicted from the value of the thrust amount of the accelerator pedal (acceleration stroke), manipulated by the driver, and the value of the vehicle speed then. Further, obtained is the difference between the value of the predicted target acceleration and the value of the actual acceleration of the vehicle detected. Based on the acquired acceleration deviation, the angle of the throttle valve is compensated so that the value of the actual acceleration matches with the value of the target acceleration.
In this control apparatus, however, the characteristic of the target acceleration to be predicted is merely set specifically from a map in advance in accordance with the relationship between the acceleration stroke and the vehicle speed. Therefore, the characteristic of the target acceleration from the map is not necessarily matched with what is intended by the driver, making it difficult to suitably control the driving power of the vehicle to match with that of the driver's intention. In addition, the characteristic from the map is always the same for the same driver, so that when the mental state of the driver or the driving environment varies, the value of the target acceleration that would satisfy the driver may not be obtained. This is likely to deteriorate the driving performance of the vehicle that the driver would feel.
There has been proposed an improved control apparatus which is designed to cope with the above-described shortcoming and ensure the efficient use of the memory in the control apparatus and the prevention of a delay in the computation of the value of the target acceleration.
This improved control apparatus has a linkless throttle valve actuated by the actuator is provided in the intake passage of the engine mounted in a vehicle. The angle of the throttle valve is controlled in accordance with the thrust amount of the accelerator pedal (acceleration stroke) manipulated by the driver. Data which determines the valve of the target acceleration corresponding to the acceleration stroke is previously stored as a map in a backup RAM. The angle of the throttle value is controlled in such a manner that the actual acceleration of the vehicle matches with the target acceleration determined by this map. Through this control, the driving power of the vehicle is controlled. According to this control apparatus, a change in acceleration stroke and the actual acceleration are detected as the degree of the acceleration requested by the driver. The data on the map is corrected so as to minimize the difference between the detected degree of the requested acceleration and the value of the target acceleration which is to be determined from the map, and the corrected data is stored in the backup RAM again. That is, mathematically, the compensation (correction) on the value of the target acceleration is performed in accordance with the level of the mentioned difference and the map is rewritten accordingly. In other words, the data of the target acceleration corresponding to the acceleration stroke is properly updated and learned.
Since learning is executed in such a way that the data of the target acceleration matches with the acceleration requested by the driver, therefore, the target acceleration which meets the driver's request is always determined. As a result, it is possible to always obtain the driving power which matches with the characteristic of the driver, regardless of the mental state of the driver and the driving environment.
According to the above-described latter control technique, however, the data of the target acceleration is learned simply by compensating (correcting) the data and rewriting the map accordingly. The data of the target acceleration is merely learned just for a certain point or a certain range of the acceleration stroke. For the driving area involving the constant speed cruising, for example, the data of the target acceleration is merely learned just for the associated range of the acceleration stroke. For the driving area involving the rapid acceleration of the vehicle, likewise, the data of the target acceleration is merely learned just for the associated range of the acceleration stroke.
As the data of the target acceleration is thus compensated or corrected only for a specific partial driving area on the map, a regional unbalance may occur in the characteristic of the rewritten map. That is, even if the compensation or correction is performed on the target acceleration for a specific range of the acceleration stroke, that compensation (correction) will not be reflected on the other range of the acceleration stroke. This causes partial discontinuity on the relationship between the acceleration stroke and the target acceleration in the characteristic of the rewritten map, so that the characteristic of the control on the vehicle's driving power may partially become discontinuous with respect to a change in acceleration stroke.
In addition, in the latter conventional control apparatus, it takes a certain time to learn the acceleration requested by the driver, raising the following shortcoming. In the case where a plurality of drivers drive a specific vehicle, when the driver of the vehicle changes from one driver to another, the directivity or preference of the new driver is apt to differ from that of the previous one. In this case, it is not possible to update the learning status of the previous driver and to immediately reflect the preference of the new driver on the driving of the vehicle. For instance, when a driver who prefers to always driving the vehicle fast is changed to the one who prefers to always driving the vehicle slowly, there is some delay until the preference of the latter driver is reflected on the driving of the vehicle.